MRI is an imaging method which excites nuclear spins of an object set in a static magnetic field with an RF (radio frequency) signal having the Larmor frequency and reconstructs an image based on MR (magnetic resonance) signals generated due to the excitation.
Examination methods of a heart by MRI include morphological observation by imaging features of a heart, observation of myocardial dynamic states (wall motion) by cine imaging, observation of perfusion states of blood flow by imaging myocardial blood flow perfusion with contrast medium, observation of myocardial viability by late contrast-enhanced imaging which performs imaging after a predetermined period elapses after injecting contrast medium, 3D (three dimensional) observation of a whole coronary artery by non-contrast enhanced imaging of the coronary artery with enhancing contrasts of blood flow and myocardium, and the like.
Imaging for a cardiac examination requires use of reference cross sections based on cardiac anatomical characteristics. The reference cross section images include various section views such as a vertical long-axis view, a horizontal long-axis view, a 2 chamber long-axis view, a 3 chamber long-axis view, a 4 chamber long-axis view and a LV (left ventricle) short-axis view in addition to axial images, coronal images and sagittal images for positioning a ROI (region of interest) and the like.
A Cardiac imaging by MRI needs acquisition of these reference cross section images at first. However, time and labor are necessary for positioning to acquire the reference cross section images because of the complex cardiac structure. Specifically, positioning a reference cross section image with reference to another reference cross section image and imaging of a positioned cross section are repeated with setting axial images as initial reference cross section images. Accordingly, more detailed procedures are prescribed as the standardized protocol for standardization of the cardiac imaging.
On the other hand, some techniques which support the positioning of the reference cross section images for cardiac imaging are suggested. For example, there is a suggested technique that 3D WH MRCA (Whole Heart MR Coronary Angiography) data is acquired so that the reference cross section images can be positioned with use of MPR (multi planar reconstructions) image data generated by MPR processing of the acquired 3D WH MRCA data. In this method, shortening of scan time is expected since imaging is not required for positioning each reference cross section image.
As another example, there is a suggested method that many axial images which cover a heart entirely are acquired by multi-slice imaging to manually set landmarks on some axial images while observing the axial images by a user. For example, landmarks are set by a user to positions of the center of aorta, the apex cordis, the mitral valve and the like on an axial image. Then, the reference cross sections necessary for cardiac imaging are automatically calculated with reference to the set landmarks.
In order to position the reference cross sections for cardiac imaging, it is necessary to repeat an imaging scan according to the number of the reference cross section images. Consequently, the work operation for positioning the reference cross sections requires time and impedes improvement of throughput in a heart examination. In addition, accuracy in positioning depends on user skill. That is, sufficient knowledge and experiment with regard to the cardiac anatomical positions are required for positioning the reference cross sections with satisfactory accuracy.
It is an object of the present invention to provide a magnetic resonance imaging apparatus and a magnetic resonance imaging method which make it possible to image a heart by positioning respective reference cross sections in the heart with practical accuracy more easily in a shorter time.